1. Field of the Invention
The invention relates to embossable films which stress whiten or craze when pressure is applied thereto. The films are especially useful for wire identification.
2. Description of the Related Art
A wide variety of materials and methods have been used to produce identification means, e.g., tags, labels and the like, for a range of applications. One type of identification device known in the art involves film or sheet material, usually in tape form, which may be imprinted using an embossing device. One embodiment is an embossable label material which changes color during embossing. This results in improved contrast of the image symbols, which are usually white, compared to the background color. Formation of this white color by embossing is typically referred to as stress-whitening. Embossed labels of this type are disclosed in U.S. Pat. Nos. 2,925,625; 2,996,822; 3,036,945; 3,650,059; 3,887,734 and 3,542,630. Material disclosed in these patents, when provided in tape form, are useful for producing labels using an embossing labeler. Labels obtained by prior art methods exhibited good contrast between image symbols and label background.
The majority of these plastic labels require polyvinyl chloride or copolymers of polyvinyl chloride. Polypropylene or polymethylmethacrylate may be incorporated therein.
All of these compositions have one distinct drawback. If the label is subjected to sufficient heat, the plastic will anneal, and the stresses caused by embossing will be released. The image thus disappears and identification is lost.
It has now been discovered that compositions of the present invention, comprising blended polymer sheets or tapes, overcome this problem and exhibit image retention at temperatures significantly higher than prior art compositions.